Process for production of polymer particles

ABSTRACT

A process for producing polymer particles from an organic solvent solution of a polymer, which includes: (a) initially introducing polymer particles into a particle producing zone, (b) introducing an organic solvent solution containing an organic solvent and having a polymer concentration of 3 to 70% by weight, onto the polymer particles which are maintained in the particle producing zone, the particle producing zone not substantially containing steam, the organic solvent solution being added in an amount of not more than 250% by weight per hour based on the amount of the polymer particles which are initially held in the particle producing zone, and stirring the polymer particles under conditions in which the organic solvent would be vaporized, (c) separately introducing a poor solvent for the polymer into the particle producing zone, the poor solvent being selected from the group consisting of benzene, toluene, xylene, pentane, hexane, octane, acetone and methyl ethyl ketone, the poor solvent being in an amount of 5 to 200% by weight based on the weight of the organic solvent in the organic solvent solution, and (d) evaporating the organic solvent and the poor solvent, while maintaining the organic solvent solution of the polymer in contact with the polymer particles which are maintained in the particle producing zone, to produce the polymer particles.

This is a division of application Ser. No. 08/391,264 filed Feb. 21,1995 U.S. Pat. No. 5,583,166, which is a continuation application ofSer. No. 08/166,805 filed Dec. 13, 1993 (now abandoned), which is acontinuation application of Ser. No. 07/927,658 filed Aug. 26, 1992 (nowabandoned), which is a continuation application of the United Statesdesignated application of International Application No. PCT/JP92/00052filed Jan. 23, 1992.

TECHNICAL FIELD

The present invention relates to a process for producing polymerparticles. More particularly, it is concerned with a process whichbasically comprises evaporating an organic solvent while keeping asolution of a polymer in the organic solvent in contact with polymerparticles to thereby obtain polymer particles, and a process forefficiently producing polymer particles (powder) which are small inparticle diameter, high in bulk density, and reduced in residual solventand of high quality, which has been developed by improving the abovebasic technique in various respects as necessary.

BACKGROUND ART

As a process for commercially producing polymers such as polycarbonate,polyarylate and polyester polycarbonate, an interfacial polycondensationmethod is preferably employed.

In the interfacial polycondensation method, for example, ofpolycarbonate, an emulsion solution obtained after completion of thereaction is subjected to a washing and separation operation to obtain amethylene chloride solution of polycarbonate. Thereafter, from themethylene chloride solution of polycarbonate (PCM), polycarbonate isisolated to produce the polycarbonate.

As a method of isolating polycarbonate from the methylene chloridesolution of polycarbonate, various ones are under investigation.

For example, a method of adding a poor solvent to the solution ofpolycarbonate (Japanese Patent Publication No. 14474/1967), a grindingmethod with a kneader, utilizing crystallization of a polycarbonatesolution (Japanese Patent Publication No. 15899/1987), a method ofthrowing into hot water (Japanese Patent Application Laid-Open No.115625/1985), and so forth are known.

All of these methods, however, are increased in plant cost, as a methodof isolating polymers such as polycarbonate, and thus have a problem inrespect of cost. Therefor in order to decrease the cost, a moresimplified isolating method is desired.

As methods for solving the problems, improved techniques are disclosedin Japanese Patent Publication No. 54329/1985 and Japanese PatentPublication No. 45648/1990.

In any of the methods disclosed therein, however, steam or nitrogen gas,etc. are needed for evaporation of methylene chloride as the solvent,and they still have a problem of recovery of removed solvent.Furthermore they have problems that only polymer particles having largeparticle diameters are obtained, and large equipment and a lot of energyare needed for removal of the solvent. Furthermore they have problemsthat water accumulates in the system, which will need an operation towithdraw the water, and at the same time, polymers obtained contain alarge amount of water.

DISCLOSURE OF INVENTION

In view of the above circumstances, the present inventors made extensiveinvestigations to develop a process for producing polymer particles,which is of low cost, more simplified, and of high productivity and highefficiency, and furthermore which provides polymer particles which aredecreased in introduction of other components into the polymer, havesmall particle diameters, have high bulk densities, and are of highquality. As a result, it has been discovered that the above objects areattained by employing the basic technique that while keeping an organicsolvent solution of polymer in contact with polymer particles underspecified conditions, the organic solvent is evaporated, and further byapplying various improved modifications onto the above basic technique.The present invention has been accomplished based on the above findings.

That is, the present invention provides a process for producing polymerparticles from an organic solvent solution of the polymer whichcomprises feeding the organic solvent solution of polymer into aparticle forming zone which does not substantially contain steam, ismaintained in an atmosphere in which the organic solvent is vaporisable,and which contains polymer particles under stirring, and evaporating theorganic solvent while keeping the solution in contact with the polymerparticles.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating an example of a basic solventremoving apparatus suitable for the practice of the process of thepresent invention.

FIG. 2 is a schematic view illustrating another example of a basicsolvent removing apparatus suitable for practice of the presentinvention.

FIG. 3 is a schematic view illustrating an example of a solvent removingapparatus suitable for practice of the process of the present invention.

FIG. 4 is a schematic view illustrating an example of a horizontal typesolvent removing apparatus suitable for practice of the process of thepresent invention

FIG. 5 is a schematic view illustrating another example of a horizontaltype solvent removing apparatus suitable for practice of the process ofthe present invention.

The symbols in the figures are as follows:

A: Solvent removing apparatus

B: Particle producing vessel

C: Jacket

D: Mixer

E: Blade of the mixer

F: Organic solvent solution of polymer

G: heater

H: Cooler

J: Recovered solvent

K: Exhaust

L: Polymer particles

N: Poor solvent

Q: Breaker

M: Motor of the mixer, motor of the breaker

P: Pressure gauge

T: Thermometer

1: Organic solvent solution feeding pipe a, b, c, d, e, f, g, h, i, j:Organic solvent solution divided feeding pipes

2: Organic solvent solution exhaust pipe

3: Exhaust valve

4: Exhaust pipe

5: Poor solvent feeding pipe (for the particle producing vessel)

BEST MODE FOR CARRYING OUT THE INVENTION

As polymers to which the process of the present invention is applied,polycarbonate and polyarylate are most suitable. In addition, variouspolymers formed by solution polymerization, such as polyesterpolycarbonate and polyamide, can be employed.

Of these, a polycarbonate solution, for example, is obtained by theusual polycondensation reaction, and can be easily produced by reactingdivalent phenol and phosgene or a carbonic acid ester compound.

As the dihydric phenol, for example, hydroquinone, 4,4'dihydroxydiphenyl, bis(4-hydroxyphenyl)alkane (bisphenol A, etc.),bis(4-hydroxyphenyl)cycloalkane, bis(4-hydroxyphenyl)oxide,bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfone,bis(4-hydroxy-phenyl)ketone, etc., and their halogen-substitutedcompounds can be listed.

As the carbonic acid ester compound, diaryl carbonate such as diphenylcarbonate, and dialkyl carbonate such as dimethyl carbonate and diethylcarbonate can be listed.

In accordance with the phosgene method, for example, most typically, itcan be obtained by reacting bisphenol A and phosgene in an inertsolvent, such as methylene chloride, in the presence of a tertiary amine(e.g., triethylamine) catalyst.

On the other hand, the polyarylate solution is obtained by the usualpolycondensation reaction and can be easily produced by reactingdihydric phenol and terephthalic acid dichloride or isophthalic aciddichloride, for example.

As the dihydric phenol, like in the above case, hydroquinone,4,4'-dihydroxydiphenyl, bis(4-hydroxyphenyl)alkane (bisphenol A, etc.),bis(4-hydroxyphenyl)cycloalkane, bis(4-hydroxyphenyl)oxide,bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfone, etc., andtheir halogen substituted compounds can be listed.

As the organic solvent to be used in the present invention, thosesubstantially inactive to the polymer, and further substantially stableat temperatures at which they are used, and capable of dissolving thepolymer can be used. However, in the case of those having a high boilingpoint, in order to achieve efficient removal through evaporation of thesolvent, it is desirable that the heating temperature of the polymersolution is increased. Thus, taking into consideration the removal ofthe organic solvent from the polymer particles, it is preferred thatorganic solvents having boiling points of not more than 200° C. be used.

As these organic solvents, in the case of polycarbonate, for example, aswell as methylene chloride which is usually preferably used,chlorine-containing solvents such as chloroform, chlorobenzene and thelike, and solvents such as dioxane, tetrahydrofuran and the like can beused.

These solvents may contain a poor solvent to the extent that no polymeris precipitated. The poor solvent includes aromatic compounds such asbenzene, toluene, xylene and the like, alkanes such as pentane, hexane,heptane, octane and the like, ketones such as acetone, methyl ethylketone and the like, and their mixed solvents. Of these, alkanes having5 to 10 carbon atoms are preferred from operation and cost, and furtherbecause they can be easily removed from the polymer. These poor solventsmay be gasified and supplied in the form of vapor, and there may beemployed either by a method in which it is supplied when the organicsolvent solution of the polymer is introduced into the particleproducing vessel or a method in which it is supplied directly to theparticle producing vessel.

The concentration of the polymer dissolved in the above solvent is 3 to70% by weight and preferably 10 to 60% by weight. If the concentrationis less than 3% by weight, the amount of the solvent to be recovered isincreased, leading to a decrease in productivity; it is not efficient.If it is more than 70% by weight, the solution becomes solid-like,leading to a decrease in fluidity, and its introduction into the solventremoving apparatus and operation undesiraly become difficult. When theconcentration of the organic solvent solution of the polymer is morethan 40% by weight, in some cases, gelation occurs; the solution may becaused to gel.

The organic solvent solution of the polymer prepared using the organicsolvent as described above is supplied to the particle producing zone(for example, the particle producing vessel and the particle producingapparatus) which is maintained in an organic solvent vaporizingatmosphere and in which there are polymer particles under stirring.

The amount of the organic solvent solution of the polymer being suppliedvaries depending on various conditions and cannot be determinedunconditionally; usually, based on the amount of the polymer particlesheld in the particle producing zone, it is not more than 250% by weightper hour preferably not more than 100% by weight per hour. If the amountsupplied is too small, productivity is decreased, and if the amountsupplied is too large, the amount of the residual solvent in the polymerparticles obtained is increased, leading to a decrease in quality, whichis not preferable.

In connection with the supplying method, the organic solvent solution ofthe polymer may be dropped or flown onto the polymer particles remainingin the particle producing vessel. It may be introduced into movingpolymer particles. Furthermore, the organic solvent solution of thepolymer may be heated and pressed, and flashed in the particle producingvessel. If the concentration of the organic solvent solution of thepolymer is high (not less than 40% by weight), in some cases, thefluidity of the organic solvent solution is somewhat decreased; in sucha case, it is desirable that the solution be introduced into theparticle producing vessel simultaneously with its withdrawal from theheater.

Next, with regard to operating conditions of the solvent removingapparatus, it suffices that the particle producing zone is maintained inan organic solvent vaporizing atmosphere; usually, the temperature ismaintained at 0 to 200° C. and preferably 30°to 150° C. If thetemperature of the particle producing zone is less than 0° C., theevaporation rate of the organic solvent is decreased, leading to adecrease in productivity, which is not preferable. If it is more than200° C., deterioration of the polymer obtained and decomposition of thesolvent undesirably start to occur.

The pressure of the particle producing zone may be any of reducedpressure, atmospheric pressure and under pressure; it is maintained at0.1 to 11 kg/cm² (absolute pressure) and preferably 0.5 to 5 kg/cm²(absolute pressure). If the pressure is less than 0.1 kg/cm² (absolutepressure), costs for vacuum operation are undesirably increased. If ismore than 11 kg/cm² (absolute pressure), the evaporation rate of theorganic solvent is decreased and a pressure particle producing vesseland so forth are required, which become disadvantageous from a viewpoint of costs.

The residence time of the polymer in the particle producing zone isusually 0.01 to 10 hours although it varies depending on the amount ofthe organic solvent of the polymer to be supplied. If the residence timeis short, the amount of the polymer particles held is decreased, andsufficient stirring and mixing are not expected, which is not desirable.If the residence time is long, an unnecessary large particle producingvessel and the like are needed, which is a disadvantage from a viewpoint of cost and is not desirable.

The present invention is characterized in that for the removal of theorganic solvent from the organic solvent solution of the polymer, theorganic solvent is evaporated while keeping the organic solvent incontact with the polymer particles. That is, in the particle producingzone, the polymer particles are introduced in advance in order toevaporate the organic solvent. With regard to the polymer to beintroduced into the particle producing zone in advance, at the beginningof the operation, polymer particles previously produced may be charged.At the stage that the stationary operation starts, polymer particlesproduced fulfills the same function as the polymer particles previouslyintroduced, permitting continuous operation, and thus the polymer can beproduced efficiently. For example, in the case of polycarbonate, as thepolycarbonate particles, polycarbonate flakes (PCF) in a flake form areused, and their particle diameters are preferably within the range of 50μm to 3 mm. If the particle diameter is less than 50 μm or more than 3mm, the polycarbonate forms a clump and becomes difficult to bepowdered, which is not desirable.

The amount of polymer particles charged, said polymer particles being tobe introduced into the particle producing zone, is not critical, butshould be determined so that both at the start of operation and at thestationary operation polymer particles flow and can be stirredhomogeneously at least when the mixer is operated. Polymer particles atthe earlier stage of operation may be the same or different.

The present invention will hereinafter be explained referring to thedrawings.

As the particle producing vessel B constituting the main part of thesolvent removing apparatus A, either a vertical one or a horizontal onecan be used any one used for mixing and stirring of fluid or powder canbe used.

Production of polycarbonate with the solvent removing apparatus of FIG.1 will be explained.

In the first place, the solvent removing apparatus A comprises a mixer Dhaving a stirring blade E to stir polycarbonate flake PCF, and aparticle producing vessel B equipped with a jacket C for controllingtemperature. In the upper part of the particle producing vessel B, thereare provided an organic solvent solution feeding pipe 1 to supply theorganic solvent solution of polycarbonate F (PCM), and an organicsolvent discharging pipe 2 to discharge an evaporated organic solventMC. There are no special limitations to the shape and so forth of thestirring blade E, and any one can be used as long as it can uniformlyand sufficiently stir the above polycarbonate flake PCF. In the figures,P indicates a pressure gage, T indicates a thermometer, and M indicatesa stirring blade driving motor.

In the process of the present invention, the aforementionedpolycarbonate flake PCF is introduced into the particle producing vesselB as described above, and the starting material of polycarbonate organicsolvent solution F (PCM) is supplied while uniformly stirring with thestirring blade E.

Then, in the solvent removing apparatus of FIG. 2, the particleproducing vessel B is preferably provided with the jacket C whichenables to control the temperature of the particle producing vessel Bwith a heating medium, in order to evaporate the organic solvent. Theparticle producing vessel B is further provided with the mixer D havingthe stirring blade E to stir polymer particles L. In the particleproducing vessel B, there are provided an organic solvent solutionfeeding pipe 1 to appropriately control the temperature of the organicsolvent solution of polymer F with the heater G and supply it, anorganic solvent discharging pipe to exhaust K 2 to discharge the organicsolvent evaporated by contact with the polymer particle L introducedinto the particle producing vessel, a cooler H to condense theevaporated and discharged organic solvent and reuse it as a recoveredsolvent J, and so forth. The particle producing vessel B and the organicsolvent solution feeding pipe 1 may be provided with poor solventfeeding pipes 5 and 6 to supply a poor solvent N, if necessary.Additionally, the particle producing vessel B is provided with adischarge pipe 4 having a discharge valve 3 to withdraw the formedpolymer particle L. In the figures, M indicates a stirring blade drivingmotor like in the aforementioned case.

For efficient production of polymer particles in the solvent removingapparatus A of FIG. 2, in the first place, the particle producing vesselB is controlled to a predetermined temperature with the jacket C inorder to maintain an atmosphere in which the organic solvent evaporates.Into the particle producing vessel B controlled to the predeterminedtemperature, the organic solvent solution of polymer F is supplied fromthe organic solvent solution feeding pipe 1, if necessary, after heatingto a predetermined temperature with the heater G. Into the particleproducing vessel B, polymer particles previously produced are introducedat an earlier stage of operation, and they are allowed to stay byuniformly stirring with the mixer D. By evaporating the organic solventwhile keeping the organic solvent solution of polymer F supplied incontact with the polymer particle L staying under uniform stirring, thepolymer particle L is formed. The polymer particle L formed in theparticle producing vessel B is withdrawn through the discharge pipe 4 byopening or closing the discharge valve 3, and then sent to thesubsequent step.

In the process for production of polymer particles of the presentinvention, polymer particles having a small particle diameter, adecreased amount of remaining solvent, and a high bulk density can beobtained by using the poor solvent N in combination.

That is to say, in the process for producing polymer particles from theorganic solvent solution of polymer, the organic solvent solution ofpolymer, containing the poor solvent for the polymer, is supplied andthe organic solvent is evaporated while keeping the solution in contactwith the above polymer particle, whereby the object can be attained.

The amount of the poor solvent added to the organic solvent solution ofpolymer, i.e., amount=(amount of poor solvent)/(amount of the polymersolution ×concentration of the polymer solution)×100%, is 5 to 50% byweight and preferably 10 to 50% by weight based on the amount of polymersolids.

If the amount of the poor solvent added is less than 5% by weight,drying properties of the particle are sometimes deteriorated, which isnot desirable. On the other hand, if it is more than 50% by weight, insome cases, the bulk density after drying is undesirably decreased.

The poor solvent is as described above, and includes aromatic compoundssuch as benzene, toluene and xylene, alkanes such as pentane, hexane,heptane, and octane, ketones such as acetone and methyl ethyl ketone,and mixed solvents thereof. Of these, alkanes having 5 to 10 carbonatoms are preferred from viewpoints of operation and cost, and furtherbecause they can be easily removed from the polymer.

Taking the solvent removing apparatus of FIG. 2 as an example, the poorsolvent N is supplied at the same time through the poor solvent feedingpipe 5 when the organic solvent solution of polymer F, containing thepoor solvent N for the polymer, is introduced into the particleproducing vessel B, or when the organic solvent solution of polymer F isintroduced into the particle producing vessel B. The poor solvent N isintroduced into the particle producing vessel B from the poor solventfeeding pipe 3 concurrently with the introduction of the organic solventsolution of polymer F into the particle producing vessel B. Forintroduction of the poor solvent N into the particle producing vessel Bfrom the poor solvent feeding pipe 6, the poor solvent N may beintroduced as it is or after gasification thereof.

Furthermore, by introducing the poor solvent into the particle producingvessel after gasification thereof, there can be obtained polymerparticles which are small in particle diameter, and further reduced inthe residual solvent and high in bulk density.

That is to say, in the process for production of polymer particles fromthe organic solvent solution of polymer, the objects can be attained byfeeding the organic solvent solution of polymer, while at the same timefeeding the poor solvent for the polymer in the amount of 5 to 200% byweight of the organic solvent of the above organic solvent solution,after gasification thereof, and evaporating the organic solvent whilekeeping the above solution in contact with the above polymer particle.The poor solvent as herein gasified is utilized as a heat source forevaporation of the above organic solvent by itself. The poor solvent isas described above.

The amount of the poor solvent fed to the organic solvent solution ofpolymer is, based on the organic solvent in the organic solvent solutionof polymer, 5 to 200% by weight and preferably 10 to 150% by weight. Ifthe amount of the poor solvent supplied is less than 5% by weight, insome cases, drying properties of the particles are undesirablydeteriorated. If it is more than 200% by weight, in some cases, the bulkdensity after drying is undesirably decreased.

Furthermore, when the organic solvent is evaporated while keeping theorganic solvent solution in contact with the polymer particles in theparticle producing vessel equipped with the mixer to stir the polymerparticles in the particle producing vessel and a breaker capable ofbreaking the polymer particles, polymer particles having a large bulkdensity and a decreased amount of residual solvent can be obtained.

That is to say, in the process for production of polymer particles fromthe organic solvent solution of polymer, the objects can be attained byintroducing the organic solvent solution of polymer into a particleproducing zone equipped with the mixer to make the polymer particlesflow and the breaker capable of breaking them, in which there arepolymer particles under stirring, and evaporating the organic solventwhile keeping the above solution in contact with polymer particles whichare being pulverized while flowing in the above particle producing zone.

Referring to the solvent removing apparatus of FIG. 3, for example,there is used a particle producing vessel B equipped with a mixer D tostir a polymer particle L and breaker Q capable of breaking the polymerparticle L. The shape of the mixer D is as described above, and theshape and so on of the breaker Q are not critical; any structure can beemployed as long as it enables to uniformly stir the polymer particle Land to break at least part of the polymer particle L. For example, themixer D is as described above, and as the breaker Q, those in a crusherform as generally employed or having a high performance rotary blade aresuitable. The mixer and the breaker may be either common or different.As other devices attached onto the particle producing vessel A, those incommon with FIG. 1 or FIG. 2 can be used.

In the process for production of polymer particles from the organicsolvent solution of polymer, by introducing polymer particles of 3 to150% by weight of the organic solvent solution of polymer into theparticle producing zone, and evaporating the organic solvent whilekeeping the organic solvent solution in contact with the polymerparticles, polymer particles having a small particle diameter, a highbulk density and excellent in quality can be produced continuously andwith high productivity.

Referring to the solvent removing apparatus of FIG. 4, for example, thepolymer particle L formed in the particle producing vessel B iswithdrawn through the discharge pipe 4 having the discharge valve 3, andsent to the subsequent step. At this step, part of the polymer particleL withdrawn is introduced into the particle producing vessel B through arecycle pipe 7, brought into contact with the organic solvent solutionof polymer, and recycled. By operating in this way, the polymer particleL can be produced continuously. As a result, the amount to be processedin the particle producing vessel B is increased and, therefore,productivity can be increased to two or three times the usual one and atthe same time, there can be obtained polymers excellent in quality.

Furthermore, when the present invention is intended to produce polymerparticles continuously and with high productivity, the object can beattained by using a horizontal particle producing vessel. That is tosay, in the process of the present invention, the organic solventsolution of polymer is introduced into the horizontal particle producingvessel having the particle producing zone which is maintained in theatmosphere that does not substantially contain steam and the organicsolvent is vaporizable, and in which there are polymer particles understirring, and evaporating the organic solvent while keeping the organicsolvent solution of polymer in contact with the above polymer particles.

In particular, the object can be attained more effectively byintroducing the organic solvent solution of polymer in such a mannerthat it is divided and introduced into the horizontal polymer producingvessel through several points, thereby evaporating the organic solvent.

FIG. 5 is a view illustrating an example of the solvent removingapparatus, suitable for practice of the process for producingcontinuously and with high productivity.

That is to say, in the solvent removing apparatus of FIG. 5, as theparticle producing vessel B, it is characterized by using a horizontalone, and the one equipped with the mixer D with a paddle to mix thepolymer particle L and having the structure (not shown) enabling a heatmedium to flow in the rotor and the paddle is preferably used. The shapeand so on of the paddle of the stirrer D is not critical; any one can beused as long as it can stir uniformly and thoroughly the polymerparticle L present in the particle producing vessel. The amount of thepolymer particle L charged, i.e., introduced into and present in theparticle producing vessel B, is not critical, but the amount should bechosen so that both at the start of operation and the stationaryoperation, at least when the mixer is operated, the polymer particleflows and is stirred uniformly.

To obtain the polymer particle with the solvent removing apparatus asdescribed above, at the beginning, the particle producing vessel B isadjusted to the predetermined temperature with the jacket C in order tomaintain it in the atmosphere that the organic solvent is vaporizable.Into the particle producing vessel B adjusted to the predeterminedtemperature, the organic solvent solution of polymer F is introducedthrough the organic solvent solution feeding pipe 1, if necessary, afterbeing heated to the predetermined temperature with the heater G. Theorganic solvent solution of polymer F may be divided and introducedthrough organic solvent solution divided feeding pipes a, b, c, d, . . ., depending on the desired production amount. In the particle producingvessel B, polymer particles produced in advance are introduced, andallowed to stay by uniformly stirring with the stirrer D, at thebeginning of operation. By evaporating the organic solvent while keepingthe organic solvent solution of polymer F introduced, into contact withthe polymer particle L staying under uniform stirring, the polymerparticle L is formed. The polymer particle L formed in the particleproducing vessel B is withdrawn through the discharge pipe 4 by openingand closing the discharge valve 3, and sent to the subsequent step.

In this way, the polymer particle L excellent in quality can beobtained.

In the process of production of the present invention, the basictechnique is such that while keeping the organic solvent solution ofpolymer in contact with the polymer particle, the organic solvent isevaporated, and by adding new techniques to the basic technique, polymerparticles (powder) having a small particle diameter, a high bulkdensity, a decreased amount of residual solvent and excellent qualitycan be produced according to an efficient method which is of low cost,is more simplified, and is of higher productivity.

In practice of the process of the present invention on a commercialscale, as the particle producing vessel, a disc drier, a paddle mixer, arotary drum type mixer, a ribbon drier, and so forth are suitably used.Of these, a particle producing vessel designed so that during theinterval between the introduction of the organic solvent solution ofpolymer and the discharge of the polymer particles, the organic solventcan be evaporated while stirring the organic solvent solution of polymerintroduced, and the polymer particles can be withdrawn successively fromthe discharge pipe, is preferably employed. For example, a Henschelmixer manufactured by Mitsui Miike Kakoki Co., Ltd., a Nauter mixermanufactured by Hosokawa Micron Co., Ltd., Turbo Sphere Mixermanufactured by Sumitomo Jukikai Kogyo Co., Ltd., a turbulizermanufactured by Hosokawa Micron Co., Ltd., a paddle drier and a feedback paddle drier manufactured by Nara Kikai Co., Ltd., an ink line disctype drier, a rotary disc T-type drier and a paddle type driermanufactured by Tsukishima Kikai Co., Ltd., a CD drier manufactured byKurimoto Tekojo Co., Ltd., a Tolus disc and a micron thermoprocessormanufactured by Hosokawa Micron Co., Ltd., a vacuum mixing dryermanufactured by Tamagawa Machinery Co., Ltd., and so on are suitable. Asequipment for mixing of particles, a kneader, a paddle mixer, a rotarydrum type mixer, a ribbon drier, a disc drier and so on are suitablyused. As the mixing blade, a helical blade, a paddle blade, a latticeblade, a paddle type blade, and so on are suitable.

Into the particle producing vessel, inert gas such as nitrogen and airmay be introduced in combination with the organic solvent solution ofpolymer within the range that does not substantially cause problems. Thesolvent removed by evaporation from the particle producing vessel may bereused by condensing and recovering with a cooler.

The polymer particle formed in the particle producing vessel iscontinuously discharged from the lower part of the particle producingvessel through the discharge pipe by opening and closing the dischargevalve, e.g., a rotary valve. It is also possible that a dam is provideddepending on the level of the polymer particle in the particle producingvessel, and it is allowed to overflow the dam. Furthermore, when theinside of the particle producing vessel is under pressure, the polymerparticle can be discharged utilizing the inner pressure. As theapparatus for discharging, for example, an apparatus provided with ascrew conveyer, for example, can be used.

The present invention is described in more detail with reference to thefollowing examples and comparative examples. First, in Examples 1 to 14and Comparative Example 1, as the polycarbonate, Toughlon A2500 producedby Idemitsu Petrochemical Co., Ltd. was used, and dissolved in methylenechloride (special grade, produced by Hiroshima Wako Junyaku Co., Ltd.)to prepare a methylene chloride solution of polycarbonate (PCM). As thepolycarbonate flake (PCF), the one obtained by sieving Toughlon FN2200(produced by Idemitsu Petrochemical Co., Ltd.) to an average particlediameter of 0.5 mm was used.

EXAMPLE 1

A versatile mixer 5 DMV manufactured by Sanei Seisakujo Co., Ltd., wascharged with 500 g of PCF, and 30% by weight of PCM was introduced withstirring at a rate of 400 g per hour. During the introduction, thetemperature was maintained at 50° C., and the pressure, at -400 mmHg.The introduction was continued for 10 hours, and after the degree ofvacuum was controlled to less than -700 mmHg and the contents werestirred for about 30 minutes, the mixer was opened and the objectiveproduct was obtained.

EXAMPLE 2

The procedure of Example 1 was repeated with the exception that theconcentration of PCM was charged to 10% by weight.

EXAMPLE 3

The procedure of Example 1 was repeated with the exception that thetemperature was maintained at 110° C., and the pressure, at 5 kg/cm².

EXAMPLE 4

A waring blender Blender 7011S manufactured by Brerbach was used, and astainless steel container No. 8525 manufactured by Eberbach was chargedwith 100 g of PCF and 30% by weight of PCM was introduced with stirringat a rate of 90 g per hour. The temperature during the introduction was60 to 70° C. The pressure was atmospheric pressure (open system). Theintroduction was continued for 5 hours, and then the container wasclosed and the degree of vacuum was controlled to less than -700 mmHg.After the contents were stirred for about 30 minutes, the objectiveproduct was obtained.

EXAMPLE 5

A 50-liter volume mixing vessel having a helical blade was charged with10 kg of PCF, and 30% by weight of PCM was introduced with stirring at arate of 9 kg per hour. During the introduction, the temperature wasmaintained at 90° C., and the pressure, at -400 mmHg. During theoperation, the flake formed by a two stage damper was withdrawn in about1.3 kg portions at 30 minute intervals. The operation was conducted for24 hours, and about 65 kg of PCF was obtained. This PCF was maintainedfor about 30 minutes at a temperature of 50° C. and a degree of vacuumof -700 mmHg to obtain the objective product.

EXAMPLE 6

The procedure of Example 1 was repeated with the exception that the rateof introduction of PCM was changed to 1,000 g per hour.

EXAMPLE 7

The procedure of Example 2 was repeated with the exception that the rateof introduction of PCM was changed to 1,000 g per hour.

EXAMPLE 8

The procedure of Example 1 was repeated with the exception that the rateof introduction of PCM was changed to 2,000 g per hour.

COMPARATIVE EXAMPLE 1

The procedure of Example 1 was repeated with the exception that theamount of PCF was changed to 50 g, and PCM was introduced at a rate of40 g per hour.

However, since the amount of PCF was too small, uniform stirring couldnot be attained, the contents became solid, and no flake could beobtained.

The flakes obtained in Examples 1 to 8 were measured for averageparticle diameter, bulk density and the amount of residual methylenechloride (MC) for the evaluation of quality thereof. The results areshown in Table 1.

EXAMPLES 9 to 14

As the particle producing vessel, a 10-liter volume (jacketed) one tothe upper part of which was directly attached a heater having a heatconductive area of 62.5 cm² (as a heat exchanger medium, 200 pound steamwas used), was used.

In the autoclave, 1,000 g of PCF was placed, and it was stirred andmaintained at 50° C. and atmospheric pressure. Then, (a) wt % of PCM wasintroduced into the heater at a rate of (b) g per hour. As the poorsolvent, n-heptane was introduced from the side part of the autoclave ata rate of (c) g per hour.

When the amount of PC in the PCM introduced reached 500 g, about 500 gof PCF was withdrawn from the bottom. This operation was repeated untilthe total operation time was 20 hours. The PCF thus obtained was driedat 50° C. and less than -700 mmHg for 30 minutes. The evaluation ofquality was conducted on the PCF withdrawn at the fourth operation.

The values of (a), (b) and (c) in Examples 9 to 14, and theconcentration of PCM introduced into the autoclave are shown in Table 2.

The flakes obtained in Examples 9 to 14 were measured for averageparticle diameter, bulk density and the amount of residual methylenechloride (MC) for the evaluation of quality thereof. The results areshown in Table 3.

                  TABLE 1                                                         ______________________________________                                                Average Particle                                                                           Bulk Density                                                                             Residual MC                                   No.     Diameter (mm)                                                                              (g/cc)     (ppm by weight)                               ______________________________________                                        Example 1                                                                             1.42         0.58       2,100                                         Example 2                                                                             1.50         0.56       2,100                                         Example 3                                                                             1.44         0.55       2,500                                         Example 4                                                                             1.48         0.52       2,400                                         Example 5                                                                             1.44         0.59       2,100                                         Example 6                                                                             1.42         0.57       2,100                                         Example 7                                                                             1.38         0.55       2,400                                         Example 8                                                                             1.35         0.57       2,500                                         ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                                       PCM Concentration                              No.        a     b        c    (wt %)                                         ______________________________________                                        Example 9  30    1,670     0   50                                             Example 10 20    1,250     0   43                                             Example 11 30    1,333     0   60                                             Example 12 30    1,670    100  50                                             Example 13 30    1,670    200  50                                             Example 14 30    1,670    500  50                                             ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                 Average Particle                                                                           Bulk Density                                                                            Residual MC                                   No.      Diameter (mm)                                                                              (g/cc)    (ppm by weight)                               ______________________________________                                        Example 9                                                                              1.40         0.55      2,100                                         Example 10                                                                             1.33         0.56      2,200                                         Example 11                                                                             1.29         0.54      2,000                                         Example 12                                                                             0.62         0.58        500                                         Example 13                                                                             0.48         0.55        450                                         Example 14                                                                             0.30         0.54        200                                         ______________________________________                                    

EXAMPLE 15

As the polymer solution, a polycarbonate solution having a concentrationof 15% by weight was prepared by dissolving polycarbonate Toughlon A2200produced by Idemitsu Petrochemical Co., Ltd., in methylene chloride(produced by Hiroshima Wako Junyaku Co., Ltd., special Grade). As thepolymer solvent removing apparatus (particle producing machine), a TurboSphere mixer (manufactured by Sumitomo Jukikai Kogyo Co., Ltd.) wasused. This solvent removing apparatus had a 80-liter volume sphericalvessel, to the lower part of which was attached a mixer blade as ananchor type structure to sweep 50% of the surface in the vessel, and inwhich a pulverizer having a blade diameter of 80 mm was provideddownwards from the upper part thereof.

In this spherical vessel, as seed powder at the time of particleproduction, 50 liters of polycarbonate powder adjusted to about 1 mm inparticle diameter was placed. The mixer blade was rotated at 100 rpm andthe pulverizer was rotated at 1,500 rpm, both in the powder layer, whileat the same time heating of the jacket was started. When the temperatureof the polycarbonate powder reached about 70° C., the abovepolycarbonate solution was introduced from the upper gas phase portionat a rate of 50 liters/hour. The pressure was controlled so as to beabout 0.8 kg/cm² (absolute pressure). After the start of operation, inorder to make the amount of powder in the vessel hold a level nearlyequal to that of the amount of powder charged at the beginning, anoperation to semicontinuously withdraw the polycarbonate powder obtainedwas conducted.

Five hours after the start of operation, the introduction of the polymersolution was stopped and the test was ended. The particle diameter ofthe polycarbonate powder obtained was consistently about 1 to 2 mm(average particle diameter 1.8 mm) during the test period, and it wasfound that the powder having a uniform particle diameter could beobtained. Measurement of the bulk density of the powder showed that thebulk density was 0.62 (g/cc) and the powder was very bulky. Furthermore,during the operation, the stirring could be conducted always in astabilized manner. After the end of the operation, the vessel was openedand the state therein was examined; it was found that almost uniformparticle production and stirring could be attained although someagglomerates were formed. Almost no attachment onto the blade and thewall surface was observed.

EXAMPLE 16

By repeating the operation of Example 15 with the exception that theconcentration of the polymer solution was changed to 25% by weight, apowder having an average particle diameter of 2.2 mm and a bulk densityof 0.52 (g/cc) could be obtained.

EXAMPLE 17

As the polymer, polycarbonate (produced by Idemitsu Petrochemical Co.,Ltd., trade name: Toughlon A2200) was used. This was dissolved inmethylene chloride (produced by Hiroshima Wako Junyaku Co., Ltd.,special grade) in a polymer concentration of about 20% by weight, toprepare a methylene chloride solution of polycarbonate. To thismethylene chloride solution of polycarbonate was added polycarbonatedissolved in heptane in 30% by weight, which were mixed to prepare anorganic solvent solution of polycarbonate (PCM). As the polycarbonateparticle (PCF), polycarbonate produced by Idemitsu Petrochemical Co.,Ltd., under the trade name of Toughlon FN2200 was used, which was sievedto adjust the average particle diameter to 0.5 mm.

A vertical container having an effective inner volume of about 4 literswas provided with a mixer having three sets of paddles. This containerwas charged with 1,000 g of PCF, and PCM was supplied with stirring at arate of 2 liters per hour. During introduction, the temperature of thecontainer was maintained at 50° C. by heating with the jacket, and thepressure was maintained at 1.3 kg/cm² abs.

In one hour from the start of introduction, the level of particles inthe container began to rise, and thus the polycarbonate particles formedwere withdrawn at a rate of 600 g per hour on the average, utilizing thevalve provided in the lower part of the container. When the particleshave consistent properties after they were withdrawn, a sample was takenout of them. The average particle diameter of the particles was measuredand found to be 0.41 mm. Then the sample was dried in a vacuum oven(temperature 130° C.) for one day and night, and its solvent content wasmeasured and found to be 63% by weight.

The particles were placed in a drier container having a volume of 200milliliters, and dried by heating at 130° C. for about 5 hours in astream of nitrogen. The solvent content of the particle dropped to0.002% by weight. Observation of the particle showed that there wereobtained particles having a lot of voids and good drying properties.

EXAMPLE 18

The procedure of Example 17 was repeated with the exception that thetype and amount of the poor solvent in the polymer solution were changedas shown in Table 4.

EXAMPLE 19

As the stirring vessel, a Turbo Sphere mixer (manufactured by SumitomoJukikai Kogyo Co., Ltd.) was used. This container was a spherical vesselhaving a volume of 8 liters, to the lower part of which was attached astirring blade as an anchor type structure to sweep 50% of the contents.This container was charged with 50 liters of PCF. To the PCF, PCM wassupplied at a rate of 50 liters per hour. Eight hours after the start ofoperation, particles formed were withdrawn as samples, which were thenmeasured for average particle diameter. The average particle diameterwas 0.33 mm, and the amount of the solvent was 32% by weight. On dryingthe sample with heated nitrogen, the amount of the solvent dropped to0.0005% by weight; the sample was thoroughly dried.

Table 5 shows the results of measurement in each item of polycarbonateparticles obtained in the preceding examples.

In accordance with the process of the present invention, there can beobtained polymer particles which have good drying properties and aregreatly decreased in the residual solvent amount. Microscopicexamination shows that the polymer particles of the present inventionhave a lot of voids.

                  TABLE 4                                                         ______________________________________                                                 Polymer Solution                                                              Polymer          Poor Solvent                                                   Concen- Amount     Amount                                                     tration Supplied   introduced                                      No.        (wt %)  (1/hr)     (wt %) Type                                     ______________________________________                                        Example 17 20      2          30     Heptane                                  Example 18 25      3          5      Heptane                                  Example 19 20      50         30     Heptane                                  ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                                Sample just after                                                             Formation                                                                       Average             After Drying                                              Particle Amount of  Amount of                                                                            Bulk                                               Diameter Solvent    Solvent                                                                              Density                                  No.       (mm)     (wt %)     (ppm)  (g/cc)                                   ______________________________________                                        Example 17                                                                              0.41     63         16     0.53                                     Example 18                                                                              0.29     51         28     0.67                                     Example 19                                                                              0.33     32          5     0.52                                     ______________________________________                                    

As the polymer for the organic solvent solution of polymer,polycarbonate (produced by Idemitsu Petrochemical Co., Ltd., Toughlon Ab2500) was used. This was dissolved in methylene chloride (produced byHiroshima Wako Junyaku Co., Ltd., special grade) in a polymerconcentration of 10 to 20% by weight to prepare a methylene chloridesolution of polycarbonate (PCM). In connection with polymer particles,as the polycarbonate flake (PCF), Toughlon FN2200, trade name, producedby Idemitsu Petrochemical Co., Ltd., was used, and sieved to adjust theaverage particle diameter to 0.5 mm.

As the particle producing vessel, a horizontal vessel (jacketed) havingan effective inner volume of about 10 liters was employed, and in itspractical use, it was provided with a mixer. First, the container wascharged with 1,000 g of PCF and operated under conditions (PCMconcentration, amount of PCM supplied, type of the poor solvent, amountof the poor solvent supplied, temperature, pressure and shape of theblade) as shown in Table 6. At the point that the amount ofpolycarbonate (PC) in the PCM supplied reached 500 g, about 500 g of thePCF was withdrawn from the bottom of the container. This operation wasrepeated and continued for 20 hours.

The PCF obtained was vacuum dried at 120° C. for 24 hours. The PCFobtained at the fourth withdrawal was measured for average particlediameter, amount of the residual solvent, and bulk density. The resultsof measurement are shown in Table 7.

In accordance with the process of the present invention (example), therecan be obtained polymer particles which have good drying properties andare greatly decreased in the amount of the residual solvent. Microscopicexamination showed that the polymer particles obtained in the examplehad a lot of voids.

                  TABLE 6                                                         ______________________________________                                               PCM           Poor Solvent                                                      Concen-  Introduction      Introduction                                       tration  Amount *.sup.1    Amount *.sup.2                            No.      (wt %)   (wt %)     Type   (wt %)                                    ______________________________________                                        Example 20                                                                             20       100        Heptane                                                                              100                                       Example 21                                                                             20       100        Heptane                                                                               30                                       Example 22                                                                             30       100        Heptane                                                                              100                                       ______________________________________                                         *.sup.1  Proportion based on the amount of the polymer particle held in       the particle producing vessel.                                                *.sup.2  Proportion based on the amount of methylene chloride in the PCM      supplied.                                                                

                  TABLE 7                                                         ______________________________________                                                 Average                                                                              Amount of Residual                                                     Particle                                                                             Solvent (ppm)  Bulk                                                      Diameter Methylene  Poor  Density                                  No.        (mm)     Chloride   Solvent                                                                             (g/cc)                                   ______________________________________                                        Example 20 0.30     <20        100   0.69                                     Example 21 0.86     <20         90   0.51                                     Example 22 0.30     <20        110   0.69                                     ______________________________________                                    

As the granulator, a twin screw kneader having an inner volume of 1.0 m³and provided with a rotor having a length of 2.0 m and a diameter of 0.1m was used. As the polymer for the organic solvent solution of polymer,polycarbonate (produced by Idemitsu Petrochemical Co., Ltd., ToughlonA2500) was used. This was dissolved in methylene chloride (produced byHiroshima Wako Junyaku Co., Ltd., special grade) in a polymerconcentration of 10 to 30% by weight to prepare a methylene chloridesolution of polycarbonate (PCM). As polymer particles at the earlierstage of the operation, polycarbonate flake (PCF, produced by IdemitsuPetrochemical Co., Ltd., Toughlon FN2200) was used and sieved to adjustthe average particle diameter to 0.5 mm.

As the granulator, the above twin screw kneader was used, and the abovePCF was introduced thereinto and the kneader was operated at 30revolutions by minute.

Operating conditions (PCM concentration, amount of PCM supplied, amountof PCF introduced, temperature and pressure) are shown in Table 8.

For evaluation of quality of the polymers obtained in the examples,average particle diameter and bulk density were measured. The results ofmeasurement are shown in Table 9.

                  TABLE 8                                                         ______________________________________                                               PCM          PCF                                                                Concen-  Introduction                                                                            Type of Introduction                                       tration  Amount    Introduc-                                                                             Amount                                    No.      (wt %)   (kg/hr)   tion    (kg/hr)                                   ______________________________________                                        Example 23                                                                             30       100       Recycle 100                                       Example 24                                                                             20       100       Recycle 100                                       Example 25                                                                             30       100       Recycle 100                                       ______________________________________                                                               PC Withdrawal                                                   Temperature             Amount                                       No.      (°C.)                                                                            Pressure      (kg/hr)                                      ______________________________________                                        Example 23                                                                             60        Atmospheric Pressure                                                                        30                                           Example 24                                                                             60        Atmospheric Pressure                                                                        20                                           Example 25                                                                             50        -200 mmHg     30                                           ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                                      Average Particle                                                              Diameter    Bulk Density                                        No.           (mm)        (g/cc)                                              ______________________________________                                        Example 23    0.42        0.68                                                Example 24    0.48        0.67                                                Example 25    0.55        0.66                                                ______________________________________                                    

EXAMPLE 26

As the particle producing vessel, a disc T type drier manufactured byTsukishima Kikai Co., Ltd. was used. This had a length of 1.8 m, aneffective volume of 50 liters, a heat conductive surface of 1.2 m² and10 paddles 18 cm in diameter, and was provided at the upper part thereofwith a hole through which the organic solvent was to be withdrawn. Hotwater maintained at 80° C. was flown through the jacket and the stirringblade.

As the polymer for the organic solvent solution of polymer,polycarbonate (produced by Idemitsu Petrochemical Co., Ltd., ToughlonA2500) was used. This was dissolved in methylene chloride (produced byHiroshima Wako Junyaku Co., Ltd., special grade) in a polymerconcentration of 10 to 30% by weight to prepare a methylene chloridesolution of polycarbonate (PCM). As the polymer particle at the start ofoperation, polycarbonate flake (PCF, produced by Idemitsu PetrochemicalCo., Ltd., Toughlon FN2200) was used, which was sieved to adjust theaverage particle diameter to 0.5 mm.

PCF in the amount of 30 kg (amount enough to hide the paddles) wascharged, and operation was conducted at a number of revolutions of 30rpm.

Into the above particle producing vessel was introduced 20% by weightPCM at 12 kg/h. The pressure was atmospheric pressure. At the time ofstationary operation, polymer particles were withdrawn from the lowerpart at 2.4 kg/h. After 48 hours, a sample was taken out, dried at 120°C. for 24 hours, and measured for bulk density and average particlediameter.

EXAMPLE 27

Three introduction conduits a, b and c were provided in the aboveparticle producing vessel, and 20% by weight PCM was introduced therethrough each at 12 kg/h. The pressure was atmospheric pressure. At thetime of stationary operation, polymer particles were withdrawn from thelower part at 7.2 kg/h. After 12 hours, a sample was taken out, dried at120° C. for 24 hours, and measured for bulk density and average particlediameter.

EXAMPLE 28

In the above particle producing vessel were provided six introductionconduits, through which 20% by weight PCM was introduced each at 12kg/h. The pressure was atmospheric pressure. At the time of stationaryoperation, polymer particles were withdrawn from the lower part at 14.4kg/h. After 6 hours, a sample was taken out, dried at 120° C. for 24hours, and measured for bulk density and average particle diameter.

EXAMPLE 29

In the above particle producing vessel were provided ten introductionconduits, through which 20% by weight PCM was introduced each at 12kg/h. The pressure was atmospheric pressure. At the time of stationaryoperation, polymer particles were withdrawn from the lower part at 24kg/h. After 6 hours, a sample was taken out, dried at 120° C. for 24hours, and measured for bulk density and average particle diameter.

EXAMPLE 30

The procedure of Example 29 was repeated with the exception that the PCMconcentration was changed to 30% by weight, and the polymer particleswere withdrawn at 36 kg/h.

EXAMPLE 31

The procedure of Example 29 was repeated with the exception that the PCMconcentration was changed to 10% by weight, and the polymer particleswere withdrawn at 12 k/h.

EXAMPLE 32

The procedure of Example 29 was repeated with the exception that thepressure was changed to -200 mmHg.

The polymer particles obtained in Examples 26 to 32 were measured forbulk density and average particle diameter, and the results are shown inTable 10.

It can be seen that in the examples of the present invention, polymerparticles having an average particle diameter of about 0.50 mm andexcellent in quality can be obtained with high productivity as seen inExamples 27 to 29.

                  TABLE 10                                                        ______________________________________                                                      Average Particle                                                              Diameter    Bulk Density                                        No.           (mm)        (g/cc)                                              ______________________________________                                        Example 26    0.50        0.62                                                Example 27    0.51        0.62                                                Example 28    0.51        0.61                                                Example 29    0.52        0.63                                                Example 30    0.51        0.61                                                Example 31    0.53        0.64                                                Example 32    0.56        0.65                                                ______________________________________                                    

As described above, in accordance with the present invention, polymerparticles can be obtained by evaporating an organic solvent whilekeeping a solution of polymer in the organic solvent in contact withpolymer particles, using a simple apparatus and operation. Further, byapplying various modifications in the process of production, ifnecessary, there can be obtained polymer particles (powder) having asmall particle diameter, a high bulk density, a small amount of residualsolvent and thus excellent in quality, with high efficiency.

Accordingly, simplification of the process is attained, and along with areduction of construction cost and running cost, production of highquality polymer in a stabilized manner can be attained.

We claim:
 1. A process for producing polymer particles from an organicsolvent solution of a polymer, which comprises:(a) initially introducingpolymer particles into a particle producing zone, (b) introducing anorganic solvent solution containing an organic solvent and having apolymer concentration of 3 to 70% by weight, onto said polymer particleswhich are maintained in said particle producing zone, said particleproducing zone not substantially containing steam, said organic solventsolution being added in an amount of not more than 100% by weight perhour based on the amount of the polymer particles which are initiallyheld in said particle producing zone, and stirring said polymerparticles under conditions in which said organic solvent would bevaporized, (c) separately introducing a poor solvent for said polymerinto said particle producing zone, said poor solvent being selected fromthe group consisting of benzene, toluene, xylene, pentane, hexane,octane, acetone and methyl ethyl ketone, said poor solvent being in anamount of 5 to 200% by weight based on the weight of said organicsolvent in said organic solvent solution, and (d) evaporating saidorganic solvent and said poor solvent, while maintaining said organicsolvent solution of said polymer in contact with said polymer particleswhich are maintained in said particle producing zone, to produce saidpolymer particles.
 2. A process for producing polymer particles from anorganic solvent solution of a polymer, which comprises:(a) initiallyintroducing polymer particles into a particle producing zone, (b)introducing an organic solvent solution containing an organic solventand having a polymer concentration of 3 to 70% by weight, onto saidpolymer particles which are maintained in said particle producing zone,said particle producing zone not substantially containing steam, saidorganic solvent solution being added in an amount of not more than 250%by weight per hour based on the amount of the polymer particles whichare initially held in said particle producing zone, and stirring saidpolymer particles under conditions in which said organic solvent wouldbe vaporized, (c) separately introducing a poor solvent for said polymerinto said particle producing zone, said poor solvent being selected fromthe group consisting of benzene, toluene, xylene, pentane, hexane,octane, acetone and methyl ethyl ketone, said poor solvent being in anamount of 5 to 200% by weight based on the weight of said organicsolvent in said organic solvent solution, said poor solvent isintroduced into said particle producing zone after gasification thereof,and (d) evaporating said organic solvent and said poor solvent, whilemaintaining said organic solvent solution of said polymer in contactwith said polymer particles which are maintained in said particleproducing zone, to produce said polymer particles.
 3. The process asclaimed in claim 1 wherein the particle producing zone is a completemixing particle producing vessel.
 4. A process for producing polymerparticles from an organic solvent solution of a polymer, whichcomprises:(a) initially introducing polymer particles into a horizontalparticle producing vessel having a horizontal particle producing zone,(b) introducing an organic solvent containing an organic solvent andhaving a polymer concentration of 3 to 70% by weight, onto said polymerparticles which are maintained in said horizontal particle producingzone, said horizontal particle producing zone not substantiallycontaining steam, said organic solvent solution being added in an amountof not more than 100% by weight per hour based on the amount of thepolymer particles which are initially held in said horizontal particleproducing zone, and stirring said polymer particles under conditions inwhich said organic solvent would be vaporized, (c) separatelyintroducing a poor solvent for said polymer into said horizontalparticle producing zone, said poor solvent being selected from the groupconsisting of benzene, toluene, xylene, pentane, hexane, octane, acetoneand methyl ethyl ketone, said poor solvent being in an amount of 5 to200% by weight based on the weight of said organic solvent in saidorganic solvent solution, and (d) evaporating said organic solvent andsaid poor solvent, while maintaining said organic solvent solution ofsaid polymer in contact with said polymer particles which are maintainedin said horizontal particle producing zone, to produce said polymerparticles.
 5. The process as claimed in claim 4 wherein said process iscontinuous and the polymer particles are stirred homogenously.
 6. Theprocess as claimed in claim 5 wherein in introducing the organic solventsolution into the horizontal particle producing vessel, the solution isdivided and introduced from a plurality of points.
 7. The process asclaimed in claim 1 wherein the organic solvent is methylene chloride. 8.The process as claimed in claim 1 wherein the polymer is selected fromthe group consisting of polycarbonate and polyarylate.
 9. The process asclaimed in claim 8 wherein said organic solvent is methylene chloride.10. The process as claimed in claim 1 wherein said polymer is selectedfrom the group consisting of polycarbonate, polyarylate and polyamide;said organic solvent is selected from the group consisting of methylenechloride, chloroform, chlorobenzene, dioxane and tetrahydrofuran; andthe process is carried out at a temperature of 0° to 200° C., at anabsolute pressure of 0.1 to 11 kg/cm² and with a residence time ofpolymer particles in the particle producing zone of 0.01 to 10 hours.11. The process as claimed in claim 10 wherein said polymer is dissolvedin said organic solvent in a concentration of 10 to 60% by weight; saidtemperature is 30 to 150° C. and said pressure is 0.5 to 5 kg/cm². 12.The process as claimed in claim 11 wherein said polymer is polycarbonatehaving a particle diameter of 50 μm to 3 μmm.
 13. The process as claimedin claim 1 wherein the process is continuous and said polymer particlesare stirred homogeneously.
 14. The process as claimed in claim 1 whereina portion of said polymer particles produced in said particle producingzone is continuously recycled to said particle producing zone.
 15. Theprocess as claimed in claim 2 wherein said organic solvent solution isin an amount of not more than 100% by weight per hour based on theamount of said polymer particles held in said polymer producing zone.